As volatile organic compounds (VOCs) become more strictly regulated in their usage, there is an ever-growing desire to provide polymeric coatings that are water based. Representative of the usage of aqueous coating dispersions is the automotive coating industry. While aqueous dispersions have several advantages relative to traditional organic solvent based dispersions such as reduction of VOC emission, reduced toxicity, lowered disposal cost, and reduced flammability, aqueous coating dispersions often suffer from low prepolymer loading in water owing to polymer immiscibility thereby complicating formulation process, cure kinetics, and application technique. Aqueous-based latex paints are exemplary of a film that fails to inhibit corrosion as containing microscopic pinholes and lacking components to suppress corrosion once initiated. In order to address prepolymer dispersibility limitations, the prepolymer is invariably derivatized to increase dispersibility in an aqueous solution. However, increasing water dispersibility of a prepolymer invariably leads to a cured coating that is more readily wet by water and often has diminished corrosion resistance. It is often desirous to make a coating electrically conductive so as to facilitate electrostatic discharge, electroplating, powder coating, or other electrostatic overlayer adhesion and application processes. While electro-coating techniques are favored for using limited or no VOCs, as well as a diminished overspray waste, the demands of requiring an aqueous dispersion of thermoset precursors to form an electrically conductive coating further complicates formulation and inevitably requires compromised corrosion resistance, handling properties, and/or dispersibility.
Curable electroconductive coatings have commonly employed a primer coating responsible for imparting corrosion resistance to the underlying substrate. Electrostatic coating generally provides improved corrosion resistance relative to spray or bath coating in providing a uniform deposition that does not suffer from coating material failing to contact recesses and complex three-dimensional substrates. A limitation associated with many conventional electrodeposition coatings is the usage of heavy metal corrosion-inhibitive pigments such as lead or chrome. The use of heavy metal corrosion-inhibitive pigments while beneficial in improving corrosion resistance of the underlying substrate create recycling and disposal problems as toxic metal particulate and aqueous leachant from such materials represent both environmental and health hazards.
Thus, there exists a need for a waterborne corrosion-resistant coating that overcomes limitations associated with conventional coatings and instead provides adhesion to a variety of substrates and tolerance to hydrocarbon fuel. There also exists a need for such a coating that can be rendered conductive and therefore useful in electrostatic charge dissipation and coating deposition and does so devoid of regulated toxic metals of lead, cobalt, cadmium, and chromium.